Optical scanner and image forming apparatus

Abstract

An optical scanner includes a single deflector to optically scan a plurality of target surfaces to be scanned. The deflector has a common rotary axis for deflecting reflective surfaces and is shared by all the beams from a plurality of light sources. The optical scanner includes photodetectors arranged to receive the beams deflected at the deflector. The beams traveling toward the deflector have an open angle in a deflecting rotation plane. A scanning optical system for guiding the deflected beam to the corresponding target surface includes two or more scanning lenses. A scanning lens proximate to the target surface passes only the beams traveling toward the same target surface. Scanning lenses proximate to the target surfaces for guiding the beams to different target surfaces have optical actions different from each other.

1. An optical scanner comprising:
 a plurality of light sources configured to emit beams including first and second beams; 
 a coupling optical system configured to couple beams emitted from the light sources; 
 a line image focusing optical system configured to focus each beam coupled to a line image extending longer in a main scan direction; 
 a deflector provided with deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, and configured to be shared by the beams from the light sources and to deflect the beams focused; 
 a scanning optical system provided with at least first and second scanning lenses, each configured to guide a corresponding beam deflected to a corresponding target surface of a plurality of target surfaces for optical scanning; and 
 a photodetector configured to receive the beams deflected at the deflector, 
 wherein 
 the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane, 
 a scanning lens proximate to one of the target surfaces, among the at least first and second scanning lenses, passes only the beams traveling toward the one of the target surfaces, and 
 the first and second scanning lenses are proximate to the target surfaces and are configured to guide the corresponding beams to different target surfaces, each scanning lens of the first and second scanning lens has a shape that asymmetrically varies along a line perpendicular to a corresponding optical axis, and the line of the first scanning lens is oriented at an angle different from the line of the second scanning lens relative to the corresponding optical axis. 
 
   
   
     2. The optical scanner according to  claim 1 , wherein the scanning lens proximate to one of the target surfaces has a power in a sub scan direction higher than a power in a sub scan direction of a scanning lens proximate to the deflector. 
   
   
     3. The optical scanner according to  claim 1 , wherein the scanning optical system arranged between the deflector and the plurality of target surfaces for guiding the beams to different target surfaces includes a reducing optical system. 
   
   
     4. The optical scanner according to  claim 1 , wherein the scanning lens proximate to one of the target surfaces has a radius of sub scan curvature on at least one surface asymmetrically varying gradually from an optical axis toward both peripheries. 
   
   
     5. The optical scanner according to  claim 1 , wherein the first and second scanning lenses proximate to the target surfaces for guiding the beams to different target surfaces have a same shape as each other and the line of the first scanning lens is oriented 180 degrees from the line of the second scanning lens relative to the corresponding optical axis. 
   
   
     6. The optical scanner according to  claim 1 , wherein the beams emitted from at least two light sources corresponding to different target surfaces are spatially separated from each other in the deflecting rotation plane on optical paths extending from the light sources to the line image focusing optical system. 
   
   
     7. The optical scanner according to  claim 1 , wherein at least two light sources corresponding to different target surfaces are integrated. 
   
   
     8. The optical scanner according to  claim 1 , wherein the photodetector configured to receive the beams deflected at the deflector receives the beams corresponding to different target surfaces. 
   
   
     9. An image forming apparatus comprising:
 an optical scanner comprising: 
 a plurality of light sources configured to emit beams including first and second beams; 
 a coupling optical system configured to couple beams emitted from the light sources; 
 a line image focusing optical system configured to focus each beam coupled to a line image extending longer in a main scan direction; 
 a deflector provided with deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, and configured to be shared by the beams from the light sources and to deflect the beams focused; 
 a scanning optical system provided with at least first and second scanning lenses, each configured to guide a corresponding beam deflected to a corresponding target surface of a plurality of photosensitive objects surfaces for optical scanning; and 
 a photodetector configured to receive the beams deflected at the deflector, 
 wherein 
 the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane, 
 a scanning lens proximate to one of the photosensitive objects, among the at least first and second scanning lenses, passes only the beams traveling toward the one of photosensitive objects, and 
 the first and second scanning lenses are proximate to the photosensitive objects and are configured to guide the corresponding beams to different photosensitive objects, each scanning lens of the first and second scanning lens has a shape that asymmetrically varies along a line perpendicular to a corresponding optical axis, and the line of the first scanning lens is oriented at an angle different from the line of the second scanning lens relative to the corresponding optical axis. 
 
   
   
     10. An optical scanner comprising:
 a plurality of light sources configured to emit beams including first and second beams; 
 a coupling optical system configured to couple beams emitted from the light sources; 
 a line image focusing optical system configured to focus each beam coupled to a line image extending longer in a main scan direction; 
 a deflector provided with deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, and configured to be shared by the beams from the light sources and to deflect the beams focused; 
 a scanning optical system provided with at least first and second scanning lenses, each configured to guide a corresponding beam deflected to a corresponding target surface of a plurality of target surfaces for optical scanning; and 
 a photodetector configured to receive the beams deflected at the deflector, 
 wherein 
 the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane, 
 a scanning lens proximate to one of the target surfaces, among the at least first and second scanning lenses, passes only the beams traveling toward the one of the target surfaces, and 
 the first and second scanning lenses are proximate to the target surfaces are configured to guide the corresponding beams to different target surfaces, and have a same shape as each other each scanning lens of the first and second scanning lens has a shape that asymmetrically varies along a line perpendicular to a corresponding optical axis, and the line of the first scanning lens is oriented 180 degrees from the line of the second scanning lens relative to the corresponding optical axis, and 
 one of the scanning lenses proximate to the target surfaces has a radius of sub scan curvature on at least one surface asymmetrically varying gradually from an optical axis toward both peripheries.